Control system for power plants comprising electric motors and prime movers



Jan. 16, 1934. H. J. COATES 1,943,369

CONTROL SYSTEM FOR POWER PLANTS COMPRISING ELECTRIC MOTORS AND PRIME MOVERS Filed Nov. 30, 1932 flhuefiwscl fizzyaze 10 7 A T TORNE) Patented Jan. 16, 1934 *UNITEB ESTATES PA TEN T 01F RICE CONTROL SYSTEM FOR POWERfPIiA'NTS COMPRISING *ELECTRIC 'MO'ITORS AND PRIME MOVERS Application "November 30, 419.32, ;Serial :No.

1644.944, and in Great "Britain December .3,

'7 Claims.

This invention relates to control :systems for :power plants comprising electriomotors adapted together with .prime .movers .to .drive ship .pro- .peller. shafts or other variable speed .loads. -In

15 such :a system it .is desirable that changes in -by the primezmover :and the .motor respectively shallbe maintainedat suitable values after such an increase inspeed, :it therefore becomes necessary .to regulate the power output of .the motor, .for example by-.decreasingthe.- field .excitationof the .-motor -or by increasing the voltage ,of the power supply to the motor. It. is. however inconvenient to .have to effect -a.-separate regulation of the motor output after each change-ofispeed, .iurthermoretheneoessary regulation cannot be readily efiected by :movement of a lever controllingthe speed. of the primemover since the position of-the controllever does not necessarily have .:a directrelationto the speeduof the prime'mover andalso the; range of"movementofthelever .over the whole speedrange is usually small. Theobjeot .of the presentinventionis to provide a sys- :tem :in which :the :necessary regulation of the .motor :output is readilyeffected upon change 01! I speed.

According to-the present invention, the necesssary'rregulation .IOf the power output of the motor upon i a change 'I'Of speed of the load is automati- 'cally effected ibya device driven at'the speeduof theiload or at aspeed proportional thereto.

*The primermovermay be an internal combustion :engine and .the motor, :which may 'be supplied with power :from a directcurrent generator driven at constant :speedand arranged for-field control, maylbe. adapted to start the engine.

The-automatic regulating means may comprise a differentialzrelaytthe excitation .of one coil of "which is a'function'of the speedof theload and "theexcitation of :another coil of which is a function of 'the position of means forzadjusting the power-supplied-by the motor.

Preferably when the motor is supplied with power from-a constantspeed. direct current. generator the 'excitation.of the-said other '0011 of "the difierentialrelayiisca lfunctiono'f the field excitation of the said generator. "The said field excitation may .be controllediby .a motor driven regulator the vmotor of which alsodrives a second regulator arranged to control .the excitation of thesaid .othercoil of the difierentialrelay and the forwardandieverse operation of the regulators may be controlled by .the differential relay.

The operation of themotorealoneto drivethe .load or to start up or to. reversethe primemover is-controlled .bya lever .orllikemember. Furthermore. it may .be arranged. 'forflthe movement of the said lever ,or-.thellike..member to a .stop position to enable vthe power supplied .to the motor to.be reduced independentlyofthespeed of the load whereby thepower may finally-be reversed to-assist in stopping theprime. mover.

The invention willnow be. described, by .way of example, with reference to the accompanying diagrammatic drawing, which shows .a control system for ship jpropulsionplant.

.'-As shown .-a propeller .1 is driven by .a emain Diesel-engine :3 through a .shaft..2, .on whichis arranged a direct current motor .4..'for;supp1ying additional power. to .the propeller .1 andiforstart- .ing up the .main Diesel-engine. .The-motor-.4.is suppliedwith power from-a direct currentgen- .erator -5 -.driven by a constant :speed .auxiliary Diesel-engine 6. The mainrDiesel: engine 3.is,pro-

vided with an air lever 7,-a fuel..lever.8,:a.speed lever 9 for regulating .the speed and-a.rever.sing wheel 10: the reversing wheel IOserves toreverse the cams of the engineand-also .servesto connect .a segment. 1 1 with a. segmentl2-or a. segment 13 according .asthe wheel isin .the Ahead as Astern position.

The generator. 5 has a shunt field-14 theexcitation of which is controlled by a regulator .15, which comprises a series resistanceprovidedwith a plurality of taps adapted .to be connected in turn to a segment 16tbyamoving,contactl'l.

The regulator is operated by means of a motor 18 througha clutch.l-9 and shat.20, which rot-atesthe contact v1'7 over the segment 16 and the taps of the regulator 15. The.motor '18 has iorwardand reverse.fields .21 and 22 energized by :closure of .contactors 123 and 24. respectively. The clutch 19 :is engaged by .energization .of .a coi1.25 by closure of-a contactor..2.6.

In addition to the regulator 15 the. shaft -20 also operates .a second regulator .27, limit segments 28 and29 associated with the motor .18, and segments 30 associated with vforwardand reverse generator field .contactors 31: and 32,-.the

segments being of the drum type. The regulator 27 is similar to the regulator 15 and comprises a series resistance provided with a plurality of taps adapted to be connected in turn to a segment 33 by a moving contact 34, which is rotated by the shaft 20. The two regulators 15 and 27 are so arranged that they both out in together and cut out together.

The forward generator field contactor 31 comprises an operating coil 35, normally open main contacts 36 and 37, normally closed interlock contacts 38, normally closed auxiliary discharge contacts 39 and two way contacts 40, 41 and 40, 42, the contacts 40, 42 normally short circuiting an economy resistance 43. The reverse generator field contactor 32 comprises an operating coil 44, normally open main contacts 45 and 46, normally closed interlock contacts 47, normally closed auxiliary discharge contacts 48 and two way contacts 49, 50 and 49, 51, the contacts 49, 51 normally short circuiting an economy resist-- ance 52. A generator field discharge resistance is connected across the contacts 39 and 48.

The regulator 27 controls the excitation of a coil 53 of a differential relay 54, which has a second coil 55 and a moving contact 56 adapted to engage one or other of two contacts 5'7 and 58. When the currents in the two coils 53 and 55 are equal the relay 54 is balanced and the moving contact rests mid-way between the contacts 57 and 58, making contact with neither. When however the current in the coil 55 exceeds the current in the coil 53 the contact 56 engages the contact 58, similarly when the current in the coil 53 exceeds the current in the coil 55 the contact 56 engages the contact 57. The contacts 58 and 57 control the forward and reverse operation of the motor 18. The coil 55 is excited from a magneto-generator 59 which is chain driven from the shaft 2 so that the excitation of the coil 55 is proportional to the speed of the shaft 2,

The motor and generator field excitation is obtained from bus bars 61 adapted to be energized from supply leads 62 and 63 by closures of a contactor 64. The contactor 64 comprises an operating coil 65, normally open main contacts 72 and 66 normally closed auxiliary contacts 67 for connecting a discharge resistance '73 across the bus bars 61, and two way contacts 68, 69 and 68, 70, the contacts 68, 7O normally short circuiting an economy resistance '71.

In order to prevent the power flowing to or from the motor 4 becoming excessive an over power and over reverse power relay 74 is provided. This relay '74 has a volt coil 75, a current coil '76 and a pair of normally closed contacts '77, which when power flow to or from the motor 4 rises above a predetermined value open to prevent operation of the motor 18. An over current relay 78 effects tripping of the contactor 64 in the event of the current fiow between the generator 5 and the motor 4 rising above a predetermined value.

The starting, stopping and reversing of the motor 4 is normally controlled by a lever '79 which is spring biased to a Neutral position in which it is shown, but which may be moved against the action of the spring either to a Start position, as represented by the broken line 80, or to a Stop position, as represented by the broken line 81. The lever '79 carries a contact 82 adapted to bridge two contacts 83 and to disengage these contacts only when the lever 79 is in the Stop position 81 and thereby to interrupt the circuit between the magneto-generator 59 and the coil 'ver '79.

55 of the differential relay 54. The lever 79 also carries a contact 84 which bridges three contacts 85, 86 and 87 when the lever is in the Start position 80. The segment 87 is connected to the operating coil of a contactor 88 closure of which short circuits part of the regulator resistance 15.

In order to start up the main Diesel engine 3 in the ahead direction, the auxiliary Diesel engine 6 running at constant speed and the regulators being in the positions shown with their resistances all in circuit, the reversing wheel 10 is set to its Ahead position and the lever 79 is held in the Start position 80. A circuit may then be traced as follows:--Supply lead 63, contacts 85, 84 and 86 of lever 79, contacts 68 and of contactor 64, operating coil 65 of contactor 64, contacts of an emergency stop 89, contacts of the over current relay 78, supply lead 62. Contactor 64 therefore closes and energizes the bus bars 61 and at the same time closes contacts 68, 69 to complete a retaining circuit from the supply lead 63, through contacts 69 and 68 of the contactor 64 and economy resistance 71 to the operating coil 65. Energization of the bus bars 61 excites the field 90 of the motor 4.

Another circuit may be traced as follows:- Supply lead 63, contacts 85, 84 and 8'7 of lever 79, operating coil of contactor 88, supply lead 62. Contactor 88 therefore closes and short circuits part of the regulator resistance 15.

A third circuit may be traced as follows:- Supply lead 63, contacts 85, 84 and 86 of lever '79, segments 11 and 12 of the reversing wheel 10, contacts 40 and 42 of the forward generator field contactor 31, operating coil 35 of contactor L 31, interlock contacts 47 of contactor 32, supply lead 62. Contactor 31 therefore closes and completes a circuit to excite the generator 5 from the bus bars 61 through contacts 36, regulator 15, generator field 14 and contacts 37. At the same time interlock contacts 38 open to prevent operation of contactor 32. Since part of the regulator resistance 15 is short circuited by the contactor 88 the voltage of the generator 5 builds up rapidly and starts the motor 4, which rotates the shaft 2 and engine 3. A circuit may be traced from the magnetogenerator 59 through the coil 55 of the differential relay 54 and contacts 82 and 83 of the le- A circuit may also be traced from the supply lead 62 through segment 33, contact 34 and the total resistance of the regulator 27 and the coil 53 of the differential relay 54 to the supply lead 63. The coil 53 is therefore weakly excited. Meanwhile the excitation of the coil 55 increases as the speed of the shaft 2 increases until finally the differential relay operates to close contacts 56 and 58. A circuit may then be traced as followsz-Supply lead 63, contacts 56 and 58 of relay 54, limit segments 29, operating coils of contactors 23 and 26, contacts '77 of over power relay 74, supply lead 62. Contactors 26 and 23 therefore close, the one completing a circuit through the operating coil 25 of the clutch 19 and the armature of the motor 18 and the other completing a circuit through the forward field 21 of the motor 18. The motor 18 now proceeds to drive the regulators 15 and 27 in the forward direction, that is so that the contacts 17 and 34 are rotated in a counter-clockwise direction. The regulator resistance 15 is thus slowly cut out and the voltage of the generator 5 is increased. In the event of the generator voltage rising too rapidly contacts 77 of the over power relay 24 open to deenergize the contactors lid operates :to close contacts56sand 5'7. .is then completed .as follows-Supply lead 63, contacts 56..and .57 lOf relay .54,.limit segments 28, operating coils of contactors .24 and .26, contacts 23 and 26 and thereby stop the ;motor '18- until "thexpower supplied' bythe'generator-5 'has 'fallen.

When the engine "3 is 'up to firing speed "fuel is admitted .and when the engine fires the lever "79 is released and returnsto the .Neutral position thereby allowing the contactor 88 :to fall open. A retaining circuit for'the contactor31 is now completed as follows :---Supp1y lead 63, seg- "ments 30,-contacts '41, 40 of the contactor 31, economy resistance 43, operating'coil35 of contactor 31.

Operation \of the motor '18 also'operates the regulator 27'to cut out its resistance, thereby increasing'the excitation or the coil 53 of therelay 54 until the relay is balanced and the "contact 5'6 breaks contact with contact 58 and'returns to its mid position; the .contactors 26 and "23 thereforefall open andthe regulators15'and 2'7 come to rest. So long as the relay 541s in its balanced position'the engineS and the motor 4 are each supplyingtheir correct shareof the total loa'd.

If the speed of the engine 3'isnow increased by movement of the lever9, the speedof the magneto-generator 59 and so the excitation of the coil "55 of the relay "54 is also increased until the relay54 again operates 'to close-its contacts "56'and 58. The -motor18 is again started up in the "forward direction to drive'the regulator '15 to 'cut out its resistance to increase the voltage of the' generator5 and the regulator 27 to cut out its resistance to increase the excitation of the 'coil'53 of the relay-'54. When the excitation of the coil '53 has risen-to that 'ofthe coil'55the relay returns toitslbalanced position and the regulators 1'5 and'27arebrought to-rest in their new positions.

If the lever 9 is operated to reduce the speed of the engine 3 the load'ofthe propeller willbe in excess of that which the :generator can supply at the voltage setting and the propeller '1 and shaft "2 will 'slow down. The reduction of speed of the magneto-generator 59 causesareduction in'the excitation of the coil55 untiltthe :relay'54 A circuit 77 of over power-relay 74, supply'llead 62. The

reverse'field22 ofthe motor ;l8 is therefore zenergized 'byiclosure of the contactor '24 and the :motor starts up to;drive':the regulatorsil5aandi27 ;in the "reverse direction. The regulator .15 cuts in its 'resistancean'd thereby reduces the voltage of the generator 5"while the regulator2'7 cuts'in its resistance and reduces the excitation of the coil :53'until the relay 54iagain-returns toiits bal- :anced position and the'regulators 15 and 27. are

brought 'to rest.

Stopping is normally performed :by cutting 011 fuel from the engine 3, the regulator 15 automatically adjusting itself underthe control of the dilferential relayt54until the propellers stop as the ship loses way. The regulator 15 is finally brought to rest in'the position shown by the inenergizing the coil=55 so-that-the relay 54 oper- "ates underthelinfiuence of 'the coil- 53 to close "contacts .56 .and 5'7. started up to drive the regulator 15't0 cut-inits resistance-and reduce the voltage of the genera- The motor 18 is thereby tor5. -When thegenerator voltage reachesvzero,

or other predetermined lowvalue '(shown on a voltmeter) and the segments '30 have interrupted the circuit to the coil 35 of contactor 3lcthelever'79 is'released, the reversing wheel 10 is moved to the *Astern.position andthe lever '79 is :held

in 'the .Start-position 80. A circuit .iscom- :pletedthrough segments/1 1 land 13 ofthe reversing wheel 10 and .theoperating coil "44 of the 'reverse contactorf32, which closes to'excite the field-l4 of the generator 5 in the reverse'direction. When the propeller has come to rest the lever79 is 'released-andreturns to the Neutral .position allowing the contactor 32 tofall open. If during excessive the over power relay '74 operates to stop 'themotor18. The relay 74 is set sothat it will only operate during the starting and stopping of -the motor 4"an'dnot 'duringrordinary speed :varii190 :ations' underthe controlof thelever 9. .Ifithe current in the circuit between the motor 4 and the generator 5 at anytime risesto anexcessive value the over current relay "78 interrupts the the rapid stopping of :the propeller the power'fiow :05

ibetween'themotor 4 and generator 5 becomes circuit through the coil of the "contactora64MJo which falls open and deenergizes the motorifield '90 and 'the generator field 14, the :discharge resistance "73 at the same time being connected across the "fields and '14. .The :eontactor 164 stop 89.

The operation in the reversezdirectionis effected by moving the reversing wheel .10 to the Asterrrposition and operating .the lever179 in .a similar manner tothat alreadytdescribed for forward .operation,1the reverse contactor -32 nowzbeing-closed instead-of the forwardccontactor 31.

Rapid reversals maybeeffectedby stopp'rngtthe propeller rapidly in the manner describedabove and retaining the lever79 in the Start position 80 until the motor 4reversesand runs up'to firing speed.

The invention may of course be. carried out.in

'various Ways-and in a modified arrangementthe "regulator controlling the field .strength of 'the generator is operated directly by a device driven by thepropellershaft to effect therequire'dreg- "ulation of the poweroutput of the motor. The device comprises a member driven :at .1the:speed of the-shaft or aspeed proportional thereto 'and asssociated by means of a slipping coupling "with asecond member which is biased to apredtermined position. The coupling 'between' the :two

"members issuch that a torque isapplied to .the

second member and tends to "rotate it against thebiasingforce, theatorque being a function of and increasing with the speed of the "first'memher. 'The biasing force exerts a torque which is a function of and increases with the displacement position,*the second member therefore takesup "a'position dependent on the speed of the shaft and the movements of the second member operate the field regulator. The slipping coupling between the two members may comprise an eddy current electric coupling, the second member being biased by a spring to a central or neutral position.

I claim:

-"'may also "be 'opened by pressing :the emergency'lla of the second 'member' from the predetermined 1. A control system for a power plant driving A1 50 a variable speed load, comprising a prime mover and an electric motor operating jointly to drive the load, each carrying a prearranged portion of the load, means for varying the speed of the prime mover, automatic means brought into operation by a change of speed of the prime mover for regulating the power output of the motor so that the latter will at all times carry a prearranged proportion of the load.

2. A control system for a power plant driving a variable speed load, comprising an electric motor and a prime mover jointly operating to carry the load, each carrying a prearranged portion thereof, means for supplying current to the motor, means for varying the speed of the prime mover according to the load requirements, means controlled by the speed of the load for automatically varying the supply of current to the motor to vary the power output thereof, the arrangement being such that the proportion of the load carried by the motor is maintained substantially constant.

3. A power plant for driving a variable speed load, such as a ship propeller shaft, comprising an electric motor, means for coupling the electric motor to the load, means for supplying current to the electric motor, a prime mover, means for coupling the prime mover to the load to operate the same jointly with the motor, means for varying the speed of the prime mover, a regulator for varying the supply of current to the motor to vary the power output thereof, rotary means operated by the load for controlling operation of the regulator to vary the power output of the motor and means for driving said rotary means from the load at a speed in proportion to the speed of the load, the arrangement being such that the motor and prime mover constantly supply prearranged proportions of the power supplied to the load.

4. A power plant for driving a variable speed load, such as a ship propeller shaft, comprising a prime mover, means for coupling the prime mover to the load, a direct current electric motor, means for coupling said motor to the load, said prime mover and the motor operating jointly to carry the load, means for varying the speed of the prime mover, an electric generator arranged to supply current to the motor, means for driving the generator at constant speed, regulating means for varying the current delivered by the generator and means operated by the load at a speed proportional to the speed of the load for operating said regulating means to increase the current output or" the load upon an increase of speed and to decrease said current output upon a decrease of speed.

5. In a power plant comprising an electric motor operating jointly with a prime mover to drive a variable speed load, such as a ship propeller shaft, a control system for maintaining the proportions of the total power supplied by the motor and the prime mover at substantially prearranged values, comprising means for varying the speed of the prime mover, a regulator for regulating the power output of the motor, means for operating said regulator, a differential relay provided with two coils for controlling said regulator operating means to increase and decrease the power output of the motor, means for supplying one of said coils with current varying with the speed of the load, means for operating said current supplying means from the load, means for supplying the other relay coil with current from an independent source, the amount of which is controlled by the position of said regulator and means for operating the latter current controlling means jointly with and in dependence upon the position of said regulator, the arrangement being such that when the differential relay is balanced by equal currents in said coils the load is proportioned as prearranged between the prime mover and the motor.

6. In a power plant comprising an electric motor operating jointly with the prime mover to drive a variable speed load, such as a ship propeller shaft, a control system for maintaining the relative proportions of the total power supplied by the motor and the prime mover at substantially prearranged values, comprising means for varying the speed of the prime mover, a direct current electric generator for supplying current to the motor, means for driving the generator at constant speed, a field regulator for controlling the excitation of the generator to vary the supply of current to the motor, an independently operated motor for operating said regulator, means controlled by the load and responsive to the speed thereof for starting the motor of the field regulator upon a change of speed of the load and means for stopping said motor when the excitation of the generator has altered the amount of current to the motor driving the load so that the latter again supplies its prearranged proportion of the total power driving the load.

'7. A power plant for driving a variable speed load, such as a ship propeller shaft, comprising a direct current electric motor, means for coupling the electric motor to the load, a prime mover, means for coupling the prime mover to the load for operation jointly with the motor, means for varying the speed of the prime mover, a direct current electric generator for supplying current 3.

to the motor, a second prime mover arranged to drive the generator at constant speed, a field regulator for controlling the excitation of the generator to vary the current supplied to the motor, an

independent motor for driving said regulator,

current operated control means for controlling the starting and stopping of the regulator motor, a second generator driven by the first prime mover for supplying current to said current operated control means in proportion to the speed of 1 the load, variation in said current controlling operation of the control means to start said regulator motor, means for supplying an independent current to said control means, which current is adapted to control operation of the control means lator motor when the first regulator has reached a predetermined position.

HERBERT JOHN COATES. 

